Preparation of levulinic acid



, transiormatio hydrate productionpl' levulinicad fr ein's ca y r bx 7 time at1 1ea'st:twicethat= 99' per centfofjthe dext" I terial is .proaueedvatmesnecm dtemp mtu ege ratio of hydrochloric acidito dextrose-being -less mangoesv for the removal of levulinic acid.

Patented Jan. 20, 1942 UNITED STATE 5 PATENT OFFICE rasrma'rroiv or LEVUIJNIC ACID WendellW. Moyer, Decatur, IlL, asslgnorto A. E.

Staley Manufacturing Company, Decatur, Ill.,

" acorporationoi'nelawarc Application Match 21, 1940, serial 1m 326,248

8 Claims.

processior'the formation of levulinic acid;

. a V V (01. 260-528) The present invention'relates to animproved of apparatus with which to carry out the process and also represents a flow'plan of the process.

.Levulinic acid- J produced heretofore I but in general the prior processes have not been suillciently workableto result in the production of levulinic acid at a price which would make the material commercially attractive; I

A principalv object of theipresentinvention carbohydrates under particular conditions. ot 1 temperature, pressure and concentrations;

- -the provision oi: an imprcved'process' by which a v 1 i relatively purelevulinic acid may lie-produced l 10 at areasonable'cost from vdextrose-containing :Arturther object of thelinventionis to provide f a levulinic acid: producing i-process by which good the "process involving usejfofsmaller fcoricehi traticnsandi q 7 a? 1 sun andtheifiemeec useof temperatures bov 75 0,

g-fr'o'inwhich the-ma v v yields of a gradeprpduct'maybeobtained,'

= acid I .for

Another, object; segmental-1's we e's.

- ment of a dextrosecontaining material with "e dilute acid solution'under such conditions asto produce levulinic; acid agranular form of humin as a byeproduct.

Still another object of the invention is theprovision ofc' a. levulinic acid process in which a dextrose-containing material is converted to I levulinic acid and by-products by treatment with a dilute acid as specified, the resulting acidic solution is filtered for removal of humin, the

filtered liquor is neutralized with respect tov the hydrochloric acid content, the neutralized solution is concentrated, the concentrated-solution is subjected to an operation "for the removal of the resulting crystalline chloride, andthe mother liquor afterthe removal "of sodium'chlo- I ride is subjectedto avacuum'distillationprocess" 1 ese and other objects ill be a consideration of the. following description of a preferred embodiment of- Qthe invention and by reference tothe drawing, in which the single figure represents a diagrammaticview observed upon In the production of levulinic. acid heretofore [various keto and aldo-hex'oses and polysacconsists of a. dextrose-containingcarbohydrate such as]; dextrose L itself; or starch. Preferably starch-is employed; althoughit will be recognized anumber of othe'r dextrose containing carf hydrates such; coniectioners, 1 1 glucose and 7 It r hydrolytic productsof starch may be utilized-f Qan'ei sugar a dis'accharide containing e'ven 'iasterjrateathan the dex- Sta'rch is apreferred starting material by reason oi, its economic availability, and for thejpurpose of. simplicity the following description of the process will be made with referencetostarch.

gA n initial step in: the'process may include chargingthe proper amount of starchand hydrochloric'acid to-a p'reheaterin'which the tempera ture of themixture-rnay be raised at atmospheric,

pressure toap'proximately 100C. I haveiou'nd that the process is benefited to a material extent by use of a dilute solution of hydrochloric acid and a particular ratio between the amount of hydrogen chloride and the amount of starch charged to the process. In accordance with my process the acid employed in converting the starch to levulinic acid contains. not morethan 3.5 per cent by weight of hydrogen chloride. Ii higher acid concentrations are used,'ditfi culties .are encountered in the physical operation of the 7 process at no beneficial gain in yield. While it iswpossible to obtain satisfactory results 'by employing an acid which isof 0.5 to 3.5,p'er cent concentration, it is preferred to utilizean acid concentration of 1.5 to 2.5: per centflstr'ength,

In' addition to the use'of a dilute acid I have found that it is of importance to properly relate the total quantity of hydrogen chloride to the dextrose'units o'i the starch. Whilea'mol ratio j of hydrogen chloride to the dextrose units of f. '1yea;=the jlevjulosebreaklng down to form levuj'linic acid at 0.35 or less is permissible, it is preferred to maintain such a ratio of between 0.15 and 0.25.

Although quite desirable the preheating step a for a sumcient period of time to complete the formation of levulinic acid. A reaction temperature between 190 C. to 200 C. is preferred.

The manner in which the reaction mixture is brought from about 100 C. to the elevated reaction temperature has a material bearing upon the success of the process. In heating the reaction mixture to around 100 C., as in the preheater, the only reaction involved is the solubilization of the starch and conversion of some of the starch to dextrose. As the temperature of the mixture is raised from 100 C. to about 200 C. I have found that proper regulation of the heating conditions will afiord definite beneficial results in the physical operation of the process. This temperature regulation includes a controlled heating operation as by live steam at a rate of 1 C. to 4 0. per minute. Even more careful temperature regulation of the order of 15 to t antilog [(25.58 1og c 12.5 10g 2.5 C. is preferred. A more rapid rise in temperature makes control of the process dimcult due to the initiation of a violent exothermic reaction in which undue quantities of humin and non-condensable gases are formed. These gases effect an excessive rise in the pressure within the digester. Thus, the, preliminary heating of the reaction mixture to the optimum range may require 'a time of the order of fifty to sixty minutes. During this initial heating period a further conversion of the starch to dextrose occurs and there is some transformation of dextrose to intermediate substances and some levulinic acid, although the time involved is insuilicient for the production of substantial quantities of levulinic acid. However, when the range of 175 C. to 215 C. is reached under the conditions of the process the levulinic acid producing reaction occurs at a very rapid rate without the formation of a type of humin which is objectionable in the process. It is probable that the controlled heating in the first part of the process from 100 C. to the maximum reaction temperature effects a breaking down of some dextrose to intermediate compounds which makes possible the quick flnal conversion at the temperature involved.

At the temperature of 175 C. to 215 C. the autoclave will have a pressure corresponding to the steam pressure at this point or slightly more than this theoretical pressure due to the formation of non-condensable gases such as carbon dioxide and carbon monoxide. As a matter of fact, the pressure may be used as an indication of the temperature in a standardized process,

since the pressure within the autoclave is more.

easily determined than the temperature.

When the temperature of the reaction mixture has been raised through the preliminary stage to the reaction range stated the temperature and pressure may be maintained substantially constant for the remainder of the process. The levulinic acid producing reaction is exothermic and requires little or no additional steam for maintaining the reactionmixture at 200 C. for completion of the process. Undue rises in temperature may be controlled by venting the digester. After the gradual heating of the starch activity, is an indication of the stage of the conversion, although I have found that this disappearance is not necessarily attended by a corresponding formation of levulinic acid. The reaction mixture is maintained at the elevated range of 175 C. to 215 C. for a. period at least twice that necessary to effect decomposition of 99 per cent of the dextrose from the reaction mixture at the temperature involved.

I have found that there is a definite relation between the important variables, temperature, acid concentration, and time of reaction in the levulinic acid process.

The time for the decomposition of 99 per cent of the dextrose in the process at any given temperature and acid concentration may be calculated approximately according to the following formula:

. per 100 grams solution, and K is temperature on the absolute scale. Accordingly, in controlling the latter stage of the process the temperature is maintained at the elevated range for a period of time equal to at least twice the time for the disappearance of 99 per cent of the dextrose as calculated by the formula. In general, it will be suflicient to maintain this temperature for a period of from 2 to 4 times the value of t derived from the formula. Within this time the maximum amount of levulinic acid will have been formed.

A further operating factor having a material bearing on the satisfactory conversion of the dextrose to levulinic acid and the recovery of this levulinic acid is in the controlled agitation of the reaction mixture in the autoclave during the digestion. Otherwise, considerable difllculty will be encountered in levulinic acid processes by the formation of a carbonaceous material termed humin. The humin tends to form in relatively large and hard lumps or as a thick crust around the walls of the converter and on top of the reaction mixture. By employing controlled heating and eiiicient mechanical agitation of the reaction mixture during the initial stage of the process and continued agitation during the heating at the relatively high temperature, there is produced a granular type of humin which does not form a crust or large lumps. The granular particles of humin produced under the conditions of my process are relatively small, hard and readily illterable. In such condition the entire charge of humin is carried out of the pressure converter along with the discharge of the reaction mixture. It then is unnecessary to open the converter for cleaning out humin. Furthermore, the granular form of humin is of such nature as to be easily separated from the mother liquor without material loss of levulinic acid. As a matter of fact, the-humin produced in this manher is of such form as to be adapted ,ior other twice the period oitime necessary to efiect decomposition of 99 per cent or the dextrose under the conditions or the process. The reaction by i which the levulinic acid is formed is exothermic and the steam which is introduced into the digester is controlled in accordance with reaction conditions within the digester so as not to permit the reaction to get out of control.- The agi- 'tatorit has the eiiect oipreventing undue local levulinic acid. This evaporation effects crystalli- 1 zation of the sodium chloride formed in the neutrallzation process andthe latter may be removed by centrifuging or otherwise. After removal of the sodium chloride; the mother liquor is subjected "to steam distillation underv vacuum, by-

a reaction and has the further highly beneficial result of producing the discrete, hard, ranular form of humin particles referred to hereinbefore.

whichoperation levulinicacid is distilledand re- 7 covered in a relatively pure form, A pressure g ftanlr 2|. wherelna'sufilcient; quantity ofsoda ash is added toreactwiththefree-hydrochloric acid presentin thelreaction :Atuthis point the liquor will have a pH of approximately Theneutralized liquor ispassed from tank 2| through line 22 to a humin filter :23. In this filter thediscrete granular form of humin is eas of not more than 1* millimeters of mercuryis desirable in keeping the distillationxtcmprature of the levulinic aciddownyto a point at which a light colored product is produced. The distillationis discontinued while. thetar residue stillis fluid and maybe removed-from the distillation equipment as'such for further treatment.

The process may be further understood by reference to a specific examplev of its operation. As indicated in. the drawing, a preheater I is 4 charged with'162 lbs. or starch through the line H.. Three hundred twenty-four lbs-oi water is passed into the preheater through the line I 2.

The liquor from the digester will contain a total oiabout 56 lbs. oi. levulinic acid, corresponding to a. yield of 48.5 per centof the yield theoretically-possible. i i

At the completionof the digestion the mixture is discharged through line to aneutralizing :iiy separatediro'm the 1i quor.-- Residual quan- 1 titles of the. liquor maybe washed from the- It will be understood that normally the water and starch will be-mixed together and introduced together into the preheater as a slurry. This mixture of water and'starch will have a Baum' of approximately 18.5 and the mixture will con-- tain approximatey 33.3 per cent starch. Commercial hydrochloric acid in the amount of 32 lbs. of 28 percent hydrogen chloride is introduced into the preheaterthrough theline l3. 1 In the preheater the resulting mixture is brought to atemperature of approximately 109 C. inany coils.

The preheatedreaction mixture then is charged through line ll to :a pressure digester It. The

digester i5 is provided with an emcient mechanisuitable manner. as b closed steam;

. r g is, whereinfthe :crystalline chloride is removed, and Ltakentromthe; processthrou h f The liquorthenispassed throughline'il toa vacuum steam distillation apparatus '32. The, Y

cal agitator Ii whichis operated in aconventiom' a1 manner by means of a rotative shatt 11 extending upwardlythrough the tankto a motor. The digester is also provided with a pressure vent V I8 whichiis of such construction as to permit the escape or gas from the digester when thepressure reaches a certain predetermined point per square inch or slightly more, thereby providhumin separated in the fllterand the humin is withdrawn'i'rom the'process through line 24. Ap-

proximately .50 lbs. ofgranular moist humin may bexremovedatthispoint. y A

. The filtratejrromfthe humilr'filter is passed through line 25 to an evaporator 28 where the concentration oi'the liquor is reducedto-such an extent as to effect crystallization of the bulk of y the sodium chloride" containedtherein. The evaporation results'in the removal of wat niora mic acidand other volatile constituentsoi rela- 'tivel low boiling point-these volatiles, beingre- 'movedthrolighline 21; j g 1 'Aiter evaporation orf the liquor to the'desired.

extent it is passed through line}! to acentriw s m. ,dist1natien 1s eerrlea tilt at less 1 l than limillim'eters o1; mercury pressure and the 1 overhead passing throughjline 83 contains the levulinic acid in a nglitflcelel-ed, relatively pureform. "The distillation is stopped while the residue in the distillation chamber is'still fluid.

ing for automatically controlling the upper temperature limit in the digester. Live. steam is introduced into the digester through the line I! to raise the temperatureot the digestion mixture.

The steam condenses to some extent'in th di-' gester in raising the-temperature of the reaction mixture and this condensation effects a further dilution of the acid. Apparently this further dilution of the acid is beneficial to the nature of the reaction. The through line I! is 'conv trolled to raisev thetemperat'ure of the :reaction mixture from- C, to around}200 C. at a rate .Various changes in the procedure-described 1 herein'may be made without departing from. the scope of the invention as defined in the append ed claims;

I claim: 1 l. The process for producing levulinic acid, which comprises providing a mixture or a dextrose-containing carbohydrate and hydrochloric acid, the'concentration of said acid being not more than 3.5 per cent hydrogen chloride. and v the mo] ratio between the hydrogenchloride and the dextrose units of said carbohydrate being not more than 0.35, subjectingsaidmix'ture to j controlled heating under pressure to raise the which averagesapproximately-T 0. per minute.

When the temperature of the' reaction mixture in the digester gets to 200," Ci-the steam is'reduced 'or' cut oil as necessary to maintain this temperatureior, a period of about 25 minutes,

this period being suiliciently long to complete the formation of levulinic acid and being more than temperature thereof to between C. and 215 r C. at a rate not exceeding 4" C. per minute; maintaining said mixture under said conditions oi temperature and pressure for aperiod of time at least'twice that necessary for the decomposition-of 99 per cent of said dextrose, agitating said v mixture during said treatment sufficiently to provide a granular type of humin, removing said humin, neutralizing the hydrochloric acid of said mixture, evaporating the neutralized mixture to crystallize the salt formed by said neutralization, removing said salt, and subjecting the reaction mixture to vacuum steam distillation for separation or levulinic acid.

2. The process of producing levulinic acid from a dextrose-producing carbohydrate, which comprises providing a mixture of said dextrose-producing carbohydrate and hydrochloric acid with a mol ratio or hydrogen chloride to dextrose units or between 0.15 and 0.25, said hydrochloric acid having a concentration of between 1.5 per cent and 2.5 per cent hydrogen chloride, subjecting said mixture to heat by live steam under pressure at a rate which will provide a temperature rise of from '1.5 C. to 2.5 C. per minute until the temperature of said mixture is between 190 C. and 200 C., maintaining the mixture at said temperature of between 190 C. to 200 C. for a longer period of time than necessary for decomposition or 99 per cent of the dextrose in said mixture, mechanically agitating the mixture during said operation, and separating levulinic acid from the reaction mixture.

3. In the production of levulinic acid, the steps which comprise subjecting a reaction mixture of a dextrose-producing carbohydrate and hydrochloric acid to heat and pressure to produce a conversion of said carbohydrates to levulinic acid and humin type compounds, and subjecting the mixture to suificient mechanical agitation during the conversion reaction to produce a granular type of humin compound.

4. In the production of levulinic acid, the steps which include subjecting a dextrose-producing carbohydrate and hydrochloric acid of a strength not more than 3.5 per cent hydrogen chloride flcient intensity to produce said humin type compounds -in granular form.

5. In the process of forming levulinic acid, the

steps which include subjecting a reaction mix- 6. The process of producing levulinic acid,

which comprises heating a starch slurry and dilute hydrochloric acid having a mol ratio to the dextrose unit of said starch of less than 0.35 under pressure with live steam to an elevated temperature of 175 C. to 215 0., controlling the heating to said elevated temperature so that the reaction mixture does not rise at an average of more than 4 C. per minute, and recovering levulinic acid from the reaction mixture.

7. The process of producing levulinic acid, which comprises reacting a dextrose-producing carbohydrate and acid to produce a reaction mixture containing levulinicacid and humin, separating the humin, neutralizing the resulting liquor to a pH of approximately 1.9, concentrating the liquor to p o uce crystallization of salt, separating salt from the liquor, and sub- ,iecting the liquor to vacuum steam distillation to recover levulinic acid. I

8. The process of forming levulinic acid, which comprises subjecting a dextrosecontaining carbohydrate to reaction with hydrochloric acid at an elevated temperature, the time involved in said reaction being at least twice that determined by the formula t= antilog [(25.58 log 0 12.5 10g 0) "-I- 22.459]

to the action of heat and pressure sumcient to etfect conversion of said carbohydrate to levulinic acid and humin type compounds, and mechanically agitating the reaction mixture during said conversion, said agitation being of sut- 

